Conventionally, in tires for a two-wheeled motor vehicle exclusively for circuit running, to ensure a gripping force during high-speed cornering, tires having relatively small proportion of grooves occupying in a tread surface (negative ratio) have been in the mainstream. Moreover, since an input force to the tires during circuit running is significantly large as compared with that during general public road running, in such tires for a two-wheeled motor vehicle, merely changing an arrangement of the grooves may cause significant deterioration of skin friction, and a maximum running speed is also high, so that a high-speed running performance is also required.
Further, due to a characteristic of a two-wheeled vehicle that corners by banking a body in a manner different from a four-wheeled vehicle, such as a passenger car and a truck, a tire for a two-wheeled motor vehicle has a tire shape in which a tire crown portion has a small curvature as compared with that of a tire for a four-wheeled vehicle and a cross section is round. Thus, according to ground contact states, when particularly a large drive force is applied, slippage portions in a ground contact surface are uneven depending on positions of a ground contact portion, and uneven wear in which specific portions are drastically worn out is likely to occur, which has been a problem.
In the prior art related to tires for a two-wheeled motor vehicle, for example, Patent Document 1 discloses a technique of arranging, on a tread surface, a bent main groove including a first groove extending toward a designated tire rotation direction while slanting toward a tread width direction outer side and a second groove extending in a reverse rotation direction from a reverse rotation direction end portion thereof while slanting toward the tread width direction outer side.